Conventional sedimentation or filtration systems operating under natural gravity have a limited capacity for separating a fluid/particle or fluid/fluid mixture, otherwise known as a feed slurry, having density differences between the distinct phases of the slurry. Therefore, industrial centrifuges that produce large centrifugal acceleration forces, otherwise known as G-levels, have advantages and thus are commonly used to accomplish separation of the light and heavy phases. Various designs of industrial centrifuges include, for example, the decanter, screen-bowl, basket, and disc centrifuge.
Industrial centrifuges rotate at very high speeds in order to produce large centrifugal acceleration forces. Several problems arise when the feed slurry is introduced into the separation pool of the centrifuge with a linear circumferential speed less than that of the centrifuge bowl.
First, the centrifugal acceleration for separation is not fully realized. The G-level might be only a fraction of what is possible. The G-level is proportional to the square of the effective acceleration efficiency. The latter is defined as the ratio of the actual linear circumferential speed of the feed slurry entering the separation pool to the linear circumferential speed of the rotating surface of the separation pool. For example, if the acceleration efficiency is 50 percent, the G-level is only 25 percent of what might be attained and the rate of separation is correspondingly reduced.
Second, the difference in circumferential linear speed, between the slurry entering the separation pool and the slurry within the separation pool which has been fully accelerated by the rotating conveyor and bowl, leads to undesirable slippage, otherwise known as velocity difference, and this creates turbulence in the slurry lying within the separation pool. Such turbulence results in resuspension of the heavy phase, equivalent to a remixing of the heavy phase material and the lighter phase material.
Third, because a portion of the separation pool is used to accelerate the feed slurry, the useful volume of the separation pool is reduced, and thus the separation efficiency of the centrifuge is lessened.
Fourth, the feed slurry often exits the feed accelerator of the centrifuge in a non-uniform flow pattern, such as in concentrated streams or jets. In a decanter centrifuge, such a non-uniform flow entering the separation pool causes remixing of the light and heavy phases, and thus reduces the separation efficiency of the centrifuge. In basket-type centrifuges, a non-uniform flow incident upon the basket causes ridges and valleys to form in the solids cake. These ridges and valleys act detrimentally upon the deliquoring of the resultant product as well as upon any required washing of the resultant product.
In view of these problems, it is desirable to incorporate feed acceleration enhancements into feed accelerators so that the feed acceleration and separation efficiency of the centrifuge are increased.